A communications cable generally includes a core of a plurality of individually insulated conductors enclosed in a sheath system. Typically, the sheath system includes a metallic shield and one or more plastic jackets. Cables such as these must be spliced together in the field. The splices are made by connecting corresponding conductors of the cables and by carrying electrical continuity across the splices between the metallic shields to provide protection against lightning, for example.
In some instances, these cables are filled with a gaseous medium such as nitrogen in order to prevent the ingress of moisture which could affect the quality of transmission. In these cables, which are referred to as pressurized cables, the gaseous medium not only fills the interstices between the conductors but also the space between components of the sheath system such as, for example, between the shield and the inner and outer plastic jackets. A splice between lengths of pressurized cables is protected by a reenterable closure which encloses the spliced conductors and an adjacent portion of each length of cable. Generally, the closure is sealed to allow the pressurized gaseous medium to extend through the splice.
Whenever a pressurized cable is connected to a non-pressurized cable, it becomes necessary to insure against the loss of the gaseous medium. Consequently, a non-pressurized cable is not directly spliced to a pressurized cable. Instead, this connection generally is accomplished by interposing an arrangement which is referred to as a cable stub assembly between the pressurized and the non-pressurized cables. The cable stub assembly is manufactured in a factory environment and is connected to the pressurized and non-pressurized cables in the field. It includes provisions for preventing the egress of the gaseous medium from the pressurized cable.
In one cable stub assembly, a portion of an outer jacket is removed from the interior of a length of cable. Then a shorter portion of a metallic shield and a still shorter portion of an inner jacket are removed to expose a core which comprises a plurality of insulated conductors. A portion of the outer jacket on each side of the exposed conductors is scuffed as is a portion of the inner jacket. A tape which adheres to the plastic of the jackets is wrapped about each scuffed portion. Over these tapes are wrapped other tapes which are stretched as they are wrapped about the underlying tapes to apply pressure thereto. A length of plastic tubing is positioned to enclose the portion of the cable which includes the exposed conductors and portions of the sheath system to each side thereof. A plastic filling material is introduced into the tubing to enclose the conductors and to adhere to the overlying tapes. Leakage persists with this kind of cable stub assembly, possibly because the scuffing and wrapping of the tapes are craft-sensitive operations.
In another prior art arrangement, turns of a tape are wrapped about the length of cable on each side of the exposed conductors. A plastic bag is disposed about the conductors and filled with a fluid plastic material. The bag is kneaded manually to cause the plastic material to be moved into the cable at each end of the exposed conductors to seal the ends of the jacketed portions. Then a heat shrinkable sleeve which had been prepositioned over one end of the cable is moved to enclose the exposed conductors and adjacent end portions of the jacket. Afterwards, the heat shrinkable sleeve is caused to be contracted about the cable end portions and the plastic bag.
Other solutions to the problem of providing pressurized cable seals have been proposed in the prior art. M. Azuma et al in a paper entitled "Development of Cable with Gas--Stoppage Dam by Polyethylene Mold Process," which appears at pages 312-315 of the Proceedings of the 25th International Wire and Cable Symposium held Nov. 16-18, 1976, proposed the use of injection molding to solve the problem of sealing a gas-pressurized cable. This process requires substantial investment in facilities and requires precise control of temperatures.
There still remains a need for an economical effective means which provides a connection between a pressurized cable and a non-pressurized cable and which prevents the escape of a gaseous medium from the pressurized cable. Any solution to this problem should comprise a cable stub assembly which is easily installed under field conditions. Also, the assembly should be one which is useable with those cables that include metallic shields and which includes facilities for carrying the continuity of the shields across the exposed conductors.